The present invention relates to a cold cathode for emitting electrons and applicable to, e.g., a field-emission display. More particularly, the present invention is concerned with a field-emission cathode for emitting electrons from its sharp tips, and a method of producing the same.
A cold cathode device structure having a number of fine cold cathodes arranged in an array (FEA hereinafter) has been reported by Spindt in Journal of Applied Physics, Vol. 39, No. 7, p. 4504, 1968. In this FEA, generally called Spindt type cold cathodes, each cold cathode consists of a conical emitter having a sharp tip and a gate electrode adjoining the emitter. The gate electrode functions to lead out a current from the emitter and to control the current.
The Spindt type FEA has an advantage that it achieves a higher current density than a hot cathode and features a small velocity distribution of emitted electrons. Another advantage of the FEA is that it reduces current noise and operates with a voltage as low as sever ten volts to 200 volts, compared to a single field-emission filter customarily included in an electron microscope. Further, while a single field-emission emitter included in an electron microscope is operable only in an ultra high vacuum atmosphere of about 10.sup.-8 Pa, the FEA can operate even in a sealed glass tube held in a vacuum atmosphere as low as about 10.sup.-4 to 10.sup.-6 Pa.
To improve the current density of the FEA, the emitters should preferably be densely arranged. However, a mask pattern used to form the emitters in a conventional procedure has a dimensional limit of the order of submicrons corresponding to the wavelength of ultraviolet rays used for exposure. This limits the density of the emitters.
Japanese Patent Laid-Open Publication No. 9-106774 discloses a field-emission display in which a mask for forming emitters is implemented by charged particles, and a method of producing the same. A high density pattern is formed for implementing self-adjustment type distance control using a Coulomb's repulsive force available with the charged particles. However, an FEA produced by such a method does not contribute to the dense arrangement of emitters because the charged particles each has a diameter of about 0.6 .mu.m even in a preferred embodiment.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-161286 and 8-77918.